1. Field of the Invention
The present invention relates to an ink jet apparatus having a pump for maintaining ink discharge from a discharge port of an ink jet head in a satisfactory condition and for discharging ink from the discharge port in order to recover such a condition, and a method of driving the ink jet apparatus.
2. Description of the Related Art
As a pump for an ink expelling means mounted in a recovery system of an ink jet recording apparatus, a plunger pump has mainly been formed, for example, into a unit. In such a pump, the contact seal surface between a piston which reciprocates inside the cylinder and the cylinder is in close contact with the inner surface of the cylinder. A seal member provided between the piston and the cylinder is in close contact with the shaft (plunger) of the piston.
In such a conventional ink jet recording apparatus, there is a case in which ink deposited on the contact seal surface of the piston and a seal member is thickened, for example, after the ink jet recording apparatus is left to stand for a long period of time. Also, since pressure is applied to the contact seal surface of the piston all the time so that the piston is brought into close contact with the inner surface of the cylinder, the piston can become stuck fast to the inner surface of the cylinder by the thickened ink. Further, since pressure is applied to seal member all the time so as to be brought into close contact with the plunger, the seal member can become stuck fast to the plunger by thickened ink.
As a result, when the pump is driven after the ink jet apparatus is left to stand for some time, the pump can be stuck fast to an extent exceeding the drive energy generated by the pump drive source, thus making the apparatus inoperable, and requiring a service call. Since this causes the reliability of the apparatus to be reduced considerably, one solution is to increase the driving force of the drive source more than is normally required so as to drive the pump unit even if the pump is stuck fast. However, extra energy is consumed when the pump is not stuck fast, and the extra energy results mainly in increased noise, which is problematical. When, in particular, a water resistant ink with a relatively high proportion of volatile components, is used, the above-described problem is more likely to occur.